All questions of Motion and Measurement of Distances for Class 6 Exam

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Understanding the SI Unit of Length
The SI (International System of Units) unit of length is essential for scientific measurements and is used globally.
Why Metre is the Standard Unit
- The metre (m) is defined as the distance light travels in a vacuum in 1/299,792,458 seconds.
- This definition ensures precision and universality in measurements across various scientific fields.
Hierarchy of Length Units
- Millimetre (mm): 1/1000 of a metre; used for small dimensions.
- Centimetre (cm): 1/100 of a metre; often used in everyday measurements.
- Kilometre (km): 1000 metres; typically used for measuring longer distances.
Global Acceptance
- The metre is recognized and adopted by scientists and engineers worldwide, facilitating international collaboration and consistency in research.
- Using a standard unit helps prevent confusion and errors in scientific communication.
Conclusion
In summary, the metre (m) is the SI unit of length, making it the correct answer to the question. Its standardization is crucial for accuracy in scientific research and global communication.

Understanding the Measurement of Curved Lines
When it comes to measuring curved lines, it's essential to select a tool that can conform to the shape of the line while providing accurate measurements. Here's why thread is the best choice:
Flexibility of Thread
- Thread is inherently flexible, allowing it to easily bend and curve along the shape of the line being measured.
- This flexibility ensures that every curve and contour can be accurately followed, capturing the true length of the curved line.
Ease of Use
- To measure a curved line, you can lay the thread along the curve, marking the start and end points.
- Once marked, you can then straighten the thread and measure it against a ruler or yardstick for an accurate length.
Comparison with Other Tools
- Ruler: A ruler is rigid and only measures straight lines. It cannot adapt to curves, making it ineffective for this purpose.
- Metal Rod: Similar to a ruler, a metal rod is also stiff and cannot bend to fit the shape of a curved line.
- Yardstick: Like a ruler, a yardstick is designed for straight measurements and lacks the flexibility needed for curves.
Conclusion
In summary, when measuring a curved line, using thread allows for precision and adaptability that other rigid tools cannot provide. Its ability to contour to the shape ensures that the measurement taken is both accurate and reliable. Thus, option 'C', thread, is indeed the best tool for this task.

To find the speed in meters per second, first convert kilometers to meters (120 km × 1000 = 120,000 meters). Then convert hours to seconds (2 hours × 3600 seconds = 7200 seconds). Average speed = Total distance / Total time = 120,000 meters / 7200 seconds ≈ 16.67 m/s.

Understanding the Motion of a Swing
A swing is a common playground equipment that showcases fascinating principles of physics, particularly in its motion. When we analyze the motion of a swing, it is important to identify the type of movement it exhibits.
What is Periodic Motion?
- Periodic motion refers to any motion that repeats itself at regular intervals.
- A swing moves back and forth in a consistent manner, returning to its starting position after a certain time.
- This regularity in its movement characterizes it as periodic.
Characteristics of a Swing's Motion
- The swing is suspended from a fixed point and moves in an arc.
- It creates a repetitive pattern, which means it goes from one side to the other and returns, resembling a cycle.
Why Not Other Types of Motion?
- Rectilinear Motion (Option A): This type of motion involves moving in a straight line. A swing does not follow a straight path; it moves in a curved arc.
- Rotational Motion (Option B): This motion involves spinning around a central point. A swing does not spin; it swings back and forth.
- Circular Motion (Option D): While a swing moves in an arc, it does not complete a full circle, which is required for circular motion.
Conclusion
- Therefore, the correct answer is option 'C' - Periodic motion, as the swing's movement is repetitive and follows a regular pattern over time.

Conversion of Meters to Millimeters
To convert meters to millimeters, you need to know that 1 meter is equal to 1000 millimeters. So, to find out how many millimeters are in 0.75 meters, you can use the following calculation:
0.75 meters x 1000 millimeters/meter = 750 millimeters
Therefore, the correct answer is:

750 mm
This means that a piece of string that is 0.75 meters long is equivalent to 750 millimeters in length.

To convert meters to centimeters, multiply by 100 (since 1 meter = 100 centimeters). Thus, 2.5 meters × 100 = 250 centimeters.